PEDS Advance Access published online on March 1, 2007
Protein Engineering Design and Selection, doi:10.1093/protein/gzm005
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Plasmid incompatibility: more compatible than previously thought?
1 Biosciences Division, Los Alamos National Laboratory, Los Alamos, USA 2 Department of Medical Sciences, University of Eastern Piedmont, Novara, Italy
4 To whom correspondence should be addressed. E-mail: amb{at}lanl.gov
It is generally accepted that plasmids containing the same origin of replication are incompatible. We have re-examined this concept in terms of the plasmid copy number, by introducing plasmids containing the same origin of replication and different antibiotic resistance genes into bacteria. By selecting for resistance to only one antibiotic, we were able to examine the persistence of plasmids carrying resistances to other antibiotics. We find that plasmids are not rapidly lost, but are able to persist in bacteria for multiple overnight growth cycles, with some dependence upon the nature of the antibiotic selected for. By carrying out the experiments with different origins of replication, we have been able to show that higher copy number leads to longer persistence, but even with low copy plasmids, persistence occurs to a significant degree. This observation holds significance for the field of protein engineering, as the presence of two or more plasmids within bacteria weakens, and confuses, the connection between screened phenotype and genotype, with the potential to wrongly assign specific phenotypes to incorrect genotypes.
Keywords: plasmid compatibility/origin of replication/antibiotic resistance
Received December 20, 2006; accepted January 9, 2007.
3 These authors contributed equally to this work.